Specialty gas manufacturers are required to perform gas analysis and certification on all gas tanks shipped to a user. Consequently, every gas tank after being filled in the production area is moved to an analytical laboratory for certification by qualified personnel.
For many years, chemical spectroscopy in industrial settings was performed off-line from the production line, with samples being extracted and taken to an analytical laboratory for analysis and interpretation. This procedure often consumed hours or days before the results were reported back to the chemical process engineer or technician.
One chemical spectroscopy system, which is performed on-line with the production line, is disclosed by Perez et al., in U.S. Pat. No. 6,748,334 issued on Jun. 8, 2004. This U.S. patent describes Fourier Transform Infrared (FTIR) Spectroscopy which bases its functionality on the principle that molecules absorb infrared light. Only the monatomic (He, Ne, Ar, etc.) and homopolar diatomic (H2, N2, O2, etc.) molecules do not absorb infrared light. Molecules only absorb infrared light at those frequencies where the infrared light affects the dipolar moment of the molecule. Molecules with a dipolar moment allow infrared photons to interact with the molecule causing excitation to higher vibrational states. The homopolar diatomic molecules do not have a dipolar moment, because the electric fields of its atoms are equal. Monatomic molecules do not have a dipolar moment because they only have one atom. Therefore, homopolar diatomic molecules and monatomic molecules do not absorb infrared light. But all other molecules do absorb infrared light.
FTIR spectroscopy generally uses a Michelson interferometer to spread a sample with the infrared light spectrum and measure the intensity of the infrared light spectrum which was not absorbed by the sample. FTIR spectroscopy observes all optical frequencies from the source simultaneously over a period of time known as a scan time.
The FTIR spectrometer measures the intensity of an infrared beam after it passes through a sample. The resulting signal, which is a time domain digital signal, is called an interferogram and contains intensity information about all frequencies present in the infrared beam. This information may be extracted by changing the signal from a time domain digital signal to a frequency domain digital signal. This change is accomplished by applying a Fourier transform over the interferogram and producing a spectral pattern known as a single beam spectrum.
Almost all molecules absorb infrared light, and each type of molecule only absorbs infrared light at certain frequencies. This property provides a unique characteristic for each molecule. It provides a way to identify the molecule type. Since each type of molecule only absorbs light at certain frequencies, it provides a unique absorption spectral pattern, or fingerprint through the entire infrared light spectrum. In this manner, the more molecules of the same gas present in the sample, the more infrared light is absorbed at specific frequencies.
The FTIR system disclosed by Perez et al. is effective in identifying moisture contamination in a sample gas. The analysis provided by the Perez system permits a user in a facility to know quickly if a gas in a cylinder starts to stray from its acceptable concentration level. The Perez system alerts the user upon detecting a concentration level change in the gas.
The Perez system, however, only detects a concentration change in the moisture level present in the sample gas. As will be described, the present invention is much more advantageous than the Perez system, because it uses a computer network with a user interface to accurately control an FTIR module. The system of the present invention with its multiple software modules analyzes and determines the concentration level of a gas in a single cylinder, or the concentration levels of multiple gases present in a batch of gas cylinders. The present invention is sufficiently accurate to provide a certification to a user that the concentration level of a gas in the cylinder shipped to his facility is within one percent of that stated on a label posted on the cylinder. These and many more advantages of the present invention will be described in detail below.